The present invention relates to a discharge element used for producing ozone from air or oxygen, charging and destaticizing powder, charging and destaticizing photoconductive insulating films used in electronic copying machines, treating plastic surfaces and the like. The present invention also relates to a discharge apparatus comprising a combination of the discharge element with a power source for driving the element, a discharge treatment apparatus comprising a combination of the discharge element with an auxiliary device, a power source and a handling device and the like.
This type of conventional discharge element has a conductive linear electrode mainly composed of a metal and provided on the surface of a ceramic insulator and a sheet electrode provided therein. When a high-frequency silent creeping discharge is produced on the surface of the ceramic insulator by applying a high-frequency high voltage between both electrodes, the linear electrode becomes worn and irregularly deformed, or the linear electrode is partially melted, scatters and adheres to the surface of the ceramic insulator. This causes a disturbance in the electric field and a deterioration in the efficiency of the electrode serving as an ion source. Apart from the melting of the electrode, this phenomenon is sometimes caused by the oxide produced by oxidation of the surface of the electrode having a low melting point and the property of easily separating.
In order to solve the above-described problem, the surfaces of the linear electrode and the ceramic insulator are coated with melted glass glazing, a ceramic thin film or the like. However, a thin coating film cannot withstand use for a long time and a thick coating film causes difficulties in generating ions due to the insulating properties between coating films and brings about the need for application of a voltage higher than that applied in a case without any coating film. In the case of a glazing layer, fine particles are generated from the glazing layer during discharge because the melting point thereof is not so high. Thus the treated gas produced when a discharge element is employed for treating the gas is sometimes contaminated with the fine particles. The contamination has a significant effect on the quality of the product to which the treated gas is applied. Particularly, when ozone is produced from boron used as a raw material by using a discharge element provided with glazing in accordance with the prior art and is used for ashing semiconductor products, if alumina is used as a ceramic insulator for the discharge element, the gas containing the produced ozone is contaminated with oxygen inevitably contained in the glazing material. This sometimes has a significant adverse effect on the quality of a semiconductor product.
In addition, in the prior art, fine ceramic represented by alumina of 92% or more purity is used as an insulator and has a conductive linear electrode integrally formed on the surface thereof and a sheet electrode integrally formed therein. A method generally used for thick film multilayer printed ceramic substrates is employed for forming both electrodes in which both electrodes are printed by a thick film technique on the insulator in the form of a green sheet before burning, pressure-welded and then metallized by burning at a high temperature for a long time in a hydrogen atmosphere. In the discharge element produced by the above method, only paste containing as a main material tungsten can be used as an electrode material because the thermal expansion coefficient of the alumina ceramic used as the insulator must agree with that of the electrode material within the wide temperature range from room temperature to about 1500.degree. C. However, since tungsten is easily oxidized at a high temperature, the electrode is worn by the oxygen contained in the atmosphere in which the discharge element is used, and the efficiency cannot be stably maintained for a long time. In addition, in the above-described method of producing a discharge element, which method is generally used for thick film multilayer printed ceramic substrates, although semiconductor ceramic is used as an electrode material, since a semiconductor literally has a high electrical resistance the efficiency deteriorates due to the generation of heat in the electrode which results in a decrease in the applied voltage in a portion of the electrode away from a feeding portion, which is caused by the voltage drop of the electrode resistance even if only the material for the electrode structure is replaced by a semiconductor material. No electric field apparatus which can be brought into practical use can thus be obtained.
The above-described methods also have the critical disadvantage that the production cost is high because the production equipment is expensive, and the production of a discharge element requires much time.
Apart from the above prior art, the ozonizer electrode shown in FIGS. 20 and 21 comprises a rod electrode 42 formed on one surface of a dielectric substrate 41 with a spacer 44 for keeping a distance l therebetween and a sheet dielectric electrode 43 formed on the other surface, the rod electrode 42 being made of conductive ceramic having electric conductivity of 10.sup.2 .OMEGA..sup.-1 cm.sup.-1 or more at 20.degree. C., the sheet dielectric electrode 43 being made of conductive ceramic or a metal, and an a.c. high-voltage power source 46 being connected between the rod electrode 42 and the sheet dielectric electrode 43. In this case, although a boron compound is suitable as a conductive ceramic material, a boron compound has a critical problem with respect to chemical contamination of the semiconductor produced when ozone is used for treating semiconductors, as described above. In addition, if the purity of the conductive ceramic is increased for obtaining high efficiency, the difference between the thermal expansion coefficients of the electrode and the substrate is increased. This mainly causes difficulties in fixing the positional relation between the dielectric substrate 41 and the rod electrode 42 and a problem with respect to the long-term stability of the electrode efficiency. Accordingly, it is an object of the present invention to solve the above problems of conventional discharge elements. Namely, the object is to improve the durability of a conductive linear electrode so as to prevent the linear electrode from being worn, irregularly deformed, by locally scattering and adhering to the surface of a ceramic insulator when a high-frequency high voltage is applied between both electrodes. The means for improving the durability brings about an improvement in the efficiency of the whole electrode and a reduction in the production cost, without deteriorating the ability to generate ozone.
It is another object of the present invention to curtail the overall cost of an apparatus comprising a discharge element by reducing the number of steps required for actually incorporating the discharge element into the apparatus. For example, in the ozone generating element shown in FIGS. 17, 18a, 18b and 19, which is formed by employing the conventional technique of producing multilayer ceramic printed substrates, a glaze coating film 24 must be provided for preventing the wearing of the linear electrode 22 formed on a surface of an alumina substrate 21 and containing tungsten as a main component. In addition, it is necessary to pass a feeding portion 22a for supplying electricity to the linear electrode 22, through a through hole 27, form a nickel layer for soldering on the surface of the feeding portion 22a, place a solder layer 25 on the nickel layer and solder a feeder 26 to the solder layer 25. In this case, the feeding portion 22a and the through hole 27 do not contribute to the generation of ozone but produce an increase in the cost caused by unnecessary increases in the sizes of the element and the container for receiving the element.
In addition, it is necessary for supplying electricity to a metal sheet electrode 23 containing tungsten as a main component to form a nickel layer 28 for soldering, place a solder layer 25 thereon and soldering a feeder 26 to the solder layer 25. The ozonizer electrode shown in FIGS. 20 and 21 also has such complicated structure and assembly and, particularly, they have a significant problem with respect to the need for a great cost for assembly including soldering. Further, when the element is sealed in a container having an inlet and an outlet and used, as in a general ozone generating apparatus, there is often the critical problem that the solder layer 25 is eroded by the ozone with the passage of time during use, and feeding finally becomes impossible.
It is a further object of the present invention to decrease the production cost of a discharge element by simplifying the method of producing the discharge element and to widen the applicability of the discharge element by widening the range of materials for the element which can be used according to the purposes of use.